This invention relates to a data transmission method and a data transmission system and particularly to those systems suitable for use in transmitting data at different transmission speeds on the same transmission line.
In the prior art, NRZ signals, bipolar signals and the like are used for serially transmitting data in the form of base band signals. However, in transmitting serial data in such form of signal wave over a long distance, a significant pulse width included in the signal waveform is dependent on the transmission speed of the data, and thus the following problems may occur.
First, since long-distance transmission of a signal on the transmission line causes the signal waveform to be distorted due to the characteristic of the line, interference between codes may occur in the binary state of the signal, preventing the binary states from being accurately discriminated.
Secondly, when data is transmitted at different transmission speeds on the same transmission line, the significant pulse width included in the transmitted signal waveform is changed depending on the transmission speeds, and thus to prevent mismatching (reflection or the like) between the transmission line characteristic and signal waveform, it is necessary to provide a circuit to terminate the line for matching to the line characteristic at each transmission speed, in the data receiving circuit, or to restrict the transmission speed.